Ball-grinding mill



P. T. LINDHARD.

BALL GRINDING MILL.

APPLICATION FILED MAY 15. 1919.

Patented Feb.15,1i92]1.

IIVVE/VTOR WITNESS.

POVL T. LINDHARD, OF BROOKLYN, NEW YORK, ASSIGNOR TO F. L. SMIDTH & C0,, 01

NEW YORK, N. 'Y., A CORPORATION OF NEW JERSEY.

i BALL-GRINDING MILL.

Specification of Letters Patent.

Patented Feb. 15, 1921.

Application filed- May 15, 1919. Serial ,No. 297,276.

To all whom it may con cern:

Be it known that I, PovL T. LrNnnAnp, a citizen of the United States, residing in the borough of Brooklyn, in the city of Xew York, in the State of New York, have 1nvented certain new and useful Improvements in'Ball-Grinding Mills, of which the following is a specification, reference being bad to the accompanying drawings, forming a part hereof.

This invention relates to a grinding mill in which free bodies are employed for grinding ore or like materials in the wet state. In mills of this type it is usual to provide at the discharge end of the mill an outlet grate through which the ground material passes after having been sub ectcd to the action of the grinding bodies. With such a grate it is diiiicult to secure a very fine degree of pulverizing since this grate 1s ex posed to the pcening action of the grinding bodies and has to be made of relatively heavy pattern. With such grate the use of small slots or openings in-the plate or between the grate bars of which the grate may be composed, is precluded. Further, the peening action of the grinding bodies tends to close such openings and ultimately preventthe discharge of material therethrough.

The object of the present invention 1s to provide a grinding mill of the type described which shall permit the material to be ground and re-ground until it reaches the desired degree of pulverization before being discharged. In the improved mill it is possible to employ a strong grate wlth sufliciently large openings to eliminate the difficulties heretofore encountered and yet secure a sufficiently fine product from the machine by preventing the discharge of the material until it is reduced to the desired state. This result is accomplished by empl ying a separate sieve orscreen onto which the material passes after having passed grinding by improved devices which constitute a feature of the present invention.

One embodiment of the invention is illustrated in the accompanying drawings, in which-- Figure 1 is a view in vertical section of a mill constructed in accordance with the present invention and provided with the improved devices for effecting a re-grinding of the material.

Fig. 2 is a transverse sectional view through the mill taken along the plane indicated by the line 2-2 of Fig. 1 and looking in the direction of the arrows.

Fig. 3 is a sectional view taken along the plane indicated by the line 3-3 of Fig. l and looking in the direction of the arrows, this figure showing particularly suitable means for returning the coarse material from the sieve to the grinding drum.

The drum a may be lined with heavy plates .7) of suitable material and be provided with a. hollow inlet trunnion c journaled in suitable bearings d, and an outlet trunnion e journaled in bearings f, substantially in the manner now employed. The drum may be rotated by application of power to a master-gear a afiiXed thereto. During the rotation of the mill the material which enters through the trunnion c is subjected to the grinding action oil free grinding bodies, usually balls. Adjacent to the discharge head 9 of the mill is mounted a transverse grate h through which the material passes after having been reduced to a size sufficient to permit it to pass through the openings in the grate. This grate is subject to the peening action of the grinding bodies and so must be of avery substantial pattern and this pattern ordinarily precludes the provision of such small openings as to insure a suiiiciently fine product. It will appear, as this description proceeds, that in the improved mill the openings in the grate b may be relatively large since the material discharged does not have its degree of pulverization dependent upon the grate. After the material passes through the openings in the grate h it is picked up by radial ribs 9 which are carried on the inner face of the outlet head 9, the material subsequently being discharged from these ribs nto the discharge trunnion c. This trunnion may carry on its inner wall a series of spiral ribs 'may be cylindrical or conical in form and is carried on the trunnion 6 so as to rotate therewith. The mesh of the sieve i is of any predetermined size and naturally all of the material which falls on the sieve and is sufliciently ground will pass through the sieve and be discharged from the hopper k. Such material as remains in lump form and is too coarse for the sieve passes into an annular trough Z carried by the screen The improved mill contemplates the return of coarse material from the screen i into the mill proper a for re-grinding. It is apparent that such return of the material may be efl'ected by many difierent mechanical devices. The particular structure illustrated herein, while well adapted for the purpose, is not the only practical method of accomplishing the result and the invention is not to be limited in such respect. In the illustrated embodiment there are employed a series of spiral tubes m which terminate with their open ends m exposed to the trough Z whereby the material discharged into the trough is picked up by the open ends of these tubes and then, during rotation of the tubes with the mill, is conveyed to a centrally located return pipe at which extends axially through the trunnion e and is supported in a central opening formed in the grate k. This tube 1?. is preferably of generally conical form and with the pipes m practica 1y constitutes a. single conduit for the return of the coarse material, to the interior of the mill a. In the returndevioes 7 described it will be evident that the screen i,

return pipe n and spiral pipes on are all connected together and are so supported on the mill as to rotate therewith. The only non-rotatable element is the hopper k. If

desired, the screen 2' may be formed with an opening 2" in its end wall and in this opening may be located a nozzle 0 for the discharge of a stream of water onto the material in the screen. This water may facilitate the screenin action. The nozzle 0 is preferably of a at type and,disposed vertically to provide a fiat, vertical spray.

From the description given it is believed that the operation of the improved mill will be apparent. The coarse material returned to the mi l is ound and re-grounduntil it is sufiiciently ne to pass through the sieve z. The grate h is of strong pattern and its openings are relatively large so that the peenmg action of the grinding bodies thereon will not quickly injure the grate or have a tendency to close the openings therein.

Various equivalent structures may be employed for accomplishing the various results described but all such structures are to be deemed within the spirit of the invention provided they fall within the scope of the appended claims.

I claim as my invention:

1. In a grinding mill, a shell having end inlet and discharge channels for the material, a grate adjacent the discharge into the discharge channel head through which the material is discharged, a screen onto which the ground material is discharged, and a return pipe from the screen to the mill and extending directly through the discharge channel and the grate for returning all ma terial which is too coarse to pass through the screen.

2. In a grinding mill, a shell having end inlet and discharge openings for the material, a grate adjacent the discharge head through which the material is discharged, a screen onto which the ground material is discharged, said screen being rotatable with the mill, a return pipe rotatable with the screen and the mill and extending through the discharge opening to pick up all material from the screen which is too coarse to pass through it and return'such material to the mill for re-grinding.

3. In a grlnding mill, a shell having trunnions and inlet and discharge openings formed in the trunnions respectively, a grate carried adjacent the discharge head throu h which the material is discharged into t e discharge-trunnion, a screen supported at the end of the discharge trunnion to receive the material therefrom, and a return pipe extending through the discharge trunnion to return the coarse material from the screen to the mill for re-grinding.

' 4. In a grinding mill, a shell having end inlet and discharge openings for the material, a grate adjacent the discharge head through which the material is discharged, a screen onto which the discharged, said screen being rotatable with the mill, a trough formed in the screen, spiral return pipes terminating inthe trough, and a return tubev carried by the mill and extending through the discharge opening and communlcating with said return pipes for ground material is the return of coarse material from the screen to the mill for re-grinding.-

5. In a grinding mill, a shell having trunnions and inlet and discharge openings formed in the trunnions, respectively, a grate carried adjacent the discharge head through which the material is discharged into the discharge trunnion, a screen supported at the end of the discharge trunnion to receive the material therefrom, and return pipes rotatable with the screen and the opening in the trunnion, a conical screen 10 mill to return the coarse material to the supported at the end of the discharge trunmill for re-grinding. nion and carrying spiral return pipes which 6. In a grinding mill, a shell having truncommunicate with the conical tube whereby 5 nions and inlet and discharge openings the coarse material on the screen is returned formed in the trunnions, respectively, a to the mill. 15 grate mounted in the mill adjacent the dis- This specification signed this 14th day of, charge head, a conical tube sup orted in the May, A. D. 1919. grate'and extending through t e discharge 

